Spaser Made of Graphene and Carbon Nanotubes

Spaser is a nanoscale source of surface plasmons comprising a plasmonic resonator and gain medium to replenish energy losses. Here we propose a carbon-based spaser design in which a graphene nanoflake (GNF) resonator is coupled to a carbon nanotube (CNT) gain element. We theoretically demonstrate that the optically excited CNT can nonradiatively transfer its energy to the localized plasmon modes of the GNF because of the near-field interaction between the modes and the CNT excitons. By calculating the localized fields of the plasmon modes and the matrix elements of the plasmon–exciton interaction, we find the optimal geometric and material parameters of the spaser that yield the highest plasmon generation rate. The results obtained may prove useful in designing robust and ultracompact coherent sources of surface plasmons for plasmonic nanocircuits

Open Resonator Electric Spaser

The inception of the plasmonic laser or spaser (surface plasmon amplification by stimulated emission of radiation) concept in 2003 provides a solution for overcoming the diffraction limit of electromagnetic waves in miniaturization of traditional lasers into the nanoscale. From then on, many spaser designs have been proposed. However, all existing designs use closed resonators. In this work, we use cavity quantum electrodynamics analysis to theoretically demonstrate that it is possible to design an electric spaser with an open resonator or a closed resonator with much weak feedback in the extreme quantum limit in an all-carbon platform. A carbon nanotube quantum dot plays the role of a gain element, and Coulomb blockade is observed. Graphene nanoribbons are used as the resonator, and surface plasmon polariton field distribution with quantum electrodynamics features can be observed. From an engineering perspective, our work makes preparations for integrating spasers into nanocircuits and/or photodynamic therapy applications

Two-Dimensional Bipyramid Plasmonic Nanoparticle Liquid Crystalline Superstructure with Four Distinct Orientational Packing Orders

Anisotropic plasmonic nanoparticles have been successfully used as constituent elements for growing ordered nanoparticle arrays. However, orientational control over their spatial ordering remains challenging. Here, we report on a self-assembled two-dimensional (2D) nanoparticle liquid crystalline superstructure (NLCS) from bipyramid gold nanoparticles (BNPs), which showed four distinct orientational packing orders, corresponding to horizontal alignment (H-NLCS), circular arrangement (C-NLCS), slanted alignment (S-NLCS), and vertical alignment (V-NLCS) of constituent particle building elements. These packing orders are characteristic of the unique shape of BNPs because all four packing modes were observed for particles with various sizes. Nevertheless, only H-NLCS and V-NLCS packing orders were observed for the free-standing ordered array nanosheets formed from a drying-mediated self-assembly at the air/water interface of a sessile droplet. This is due to strong surface tension and the absence of particle–substrate interaction. In addition, we found the collective plasmonic coupling properties mainly depend on the packing type, and characteristic coupling peak locations depend on particle sizes. Interestingly, surface-enhanced Raman scattering (SERS) enhancements were heavily dependent on the orientational packing ordering. In particular, V-NLCS showed the highest Raman enhancement factor, which was about 77-fold greater than the H-NLCS and about 19-fold greater than C-NLCS. The results presented here reveal the nature and significance of orientational ordering in controlling plasmonic coupling and SERS enhancements of ordered plasmonic nanoparticle arrays

Shape Transformation of Constituent Building Blocks within Self-Assembled Nanosheets and Nano-origami

Self-assembly of nanoparticles represents a simple yet efficient route to synthesize designer materials with unusual properties. However, the previous assembled structures whether by surfactants, polymer, or DNA ligands are “static” or “frozen” building block structures. Here, we report the growth of transformable self-assembled nanosheets which could enable reversible switching between two types of nanosheets and even evolving into diverse third generation nanosheet structures without losing pristine periodicity. Such <i>in situ</i> transformation of nanoparticle building blocks can even be achieved in a free-standing two-dimensional system and three-dimensional origami. The success in such <i>in situ</i> nanocrystal transformation is attributed to robust “plant-cell-wall-like” ion-permeable reactor arrays from densely packed polymer ligands, which spatially define and confine nanoscale nucleation/growth/etching events. Our strategy enables efficient fabrication of nanocrystal nanosheets with programmable building blocks for innovative applications in adaptive tactile metamaterials, optoelectronic devices, and sensors

Free-Standing Plasmonic-Nanorod Superlattice Sheets

The self-assembly of monodisperse inorganic nanoparticles into highly ordered arrays (superlattices) represents an exciting route to materials and devices with new functions. It allows programming their properties by varying the size, shape, and composition of the nanoparticles, as well as the packing order of the assemblies. While substantial progress has been achieved in the fabrication of superlattice materials made of nanospheres, limited advances have been made in growing similar materials with anisotropic building blocks, which is particularly true for free-standing two-dimensional superlattices. In this paper, we report the controlled growth of free-standing, large-area, monolayered gold-nanorod superlattice sheets by polymer ligands in an entropy-driven interfacial self-assembly process. Furthermore, we experimentally characterize the plasmonic properties of horizontally aligned sheets (H-sheets) and vertically aligned sheets (V-sheets) and show that observed features can be well described using a theoretical model based on the discrete-dipole approximation. Our polymer-ligand-based strategy may be extended to other anisotropic plasmonic building blocks, offering a robust and inexpensive avenue to plasmonic nanosheets for various applications in nanophotonic devices and sensors

Visualization 2: Optical Bloch oscillations and Zener tunneling of Airy beams in ionic-type photonic lattices

Optical Bloch oscillations of Airy beam in lattice 2 Originally published in Optics Express on 08 August 2016 (oe-24-16-18332

Visualization 1: Optical Bloch oscillations and Zener tunneling of Airy beams in ionic-type photonic lattices

Optical Bloch oscillations of Airy beam in lattice 1 Originally published in Optics Express on 08 August 2016 (oe-24-16-18332

Large-Scale Self-Assembly and Stretch-Induced Plasmonic Properties of Core–Shell Metal Nanoparticle Superlattice Sheets

We report on a facile interfacial self-assembly approach to fabricate large-scale metal nanoparticle superlattice sheets from nonspherical core–shell nanoparticles, which exhibited reversible plasmonic responses to repeated mechanical stretching. Monodisperse Au@Ag nanocubes (NCs) and Au@Ag nanocuboids (NBs) could be induced to self-assembly at the hexane/water interface, forming uniform superlattices up to at least ∼13 cm² and giving rise to mirror-like reflection. Such large-area mirror-like superlattice sheets exhibited reversible plasmonic responses to external mechanical strains. Under stretching, the dominant plasmonic resonance peak for both NB and NC superlattice sheets shifted to blue, following a power-law function of the applied strain. Interestingly, the power-law exponent (or the decay rate) showed a strong shape dependence, where a faster rate was observed for NB superlattice sheets than that for NC superlattice sheets

Giant Plasmene Nanosheets, Nanoribbons, and Origami

We introduce <i>Plasmene</i> in analogy to grapheneas free-standing, one-particle-thick, superlattice sheets of nanoparticles (“meta-atoms”) from the “plasmonic periodic table”, which has implications in many important research disciplines. Here, we report on a general bottom-up self-assembly approach to fabricate giant plasmene nanosheets (<i>i.e.</i>, plasmene with nanoscale thickness but with macroscopic lateral dimensions) as thin as ∼40 nm and as wide as ∼3 mm, corresponding to an aspect ratio of ∼75 000. In conjunction with top–down lithography, such robust giant nanosheets could be milled into one-dimensional nanoribbons and folded into three-dimensional origami. Both experimental and theoretical studies reveal that our giant plasmene nanosheets are analogues of graphene from the plasmonic nanoparticle family, simultaneously possessing unique structural features and plasmon propagation functionalities

Ultrathin 2D Transition Metal Carbides for Ultrafast Pulsed Fiber Lasers

Two-dimensional (2D) materials, such as graphene, transition metal dichalcogenides, and black phosphorus, have attracted intense interest for applications in ultrafast pulsed laser generation, owing to their strong light–matter interactions and large optical nonlinearities. However, due to the mismatch of the bandgap, many of these 2D materials are not suitable for applications at near-infrared (NIR) waveband. Here, we report nonlinear optical properties of 2D α-Mo₂C crystals and the usage of 2D α-Mo₂C as a new broadband saturable absorber for pulsed laser generation. It was found that 2D α-Mo₂C crystals have excellent saturable absorption properties in terms of largely tunable modulation depth and very low saturation intensity. In addition, ultrafast carrier dynamic results of 2D α-Mo₂C reveal an ultrashort intraband carrier recovery time of 0.48 ps at 1.55 μm. By incorporating 2D α-Mo₂C saturable absorber into either an Er-doped or Yb-doped fiber laser, we are able to generate ultrashort pulses with very stable operation at central wavelengths of 1602.6 and 1061.8 nm, respectively. Our experimental results demonstrate that 2D α-Mo₂C can be a promising broadband nonlinear optical media for ultrafast optical applications